The Carlson process is currently used in xerographic copiers and laser printers. In this process, a non-conducting drum is uniformly charged. This drum has a high electrical resistivity in the absence of light and, therefore, can retain the uniform charge for a considerable period of time (on the order of seconds). A light beam, originating as an analog signal (as in a copier) or as a digital signal (as in a laser printer), impinges on the drum thereby changing the drum's electrical resistivity at that point. This change in electrical resistivity, in turn, allows the charge deposited on the drum's surface at that point to discharge to ground potential. In this manner, a latent image is formed on the drum.
After the latent image is formed on the drum, the drum is exposed to a toner. The regions of high charge on the drum attract toner particles, and the regions without charge are left without toner particles. Subsequently, an oppositely charged piece of paper attracts the toner particles from the drum and holds the toner until it is heated and permanently pressed into the paper (a process called fusing). All copiers and laser printers now on the market using the Carlson process require an optical photoconductor, a light exposing apparatus, and a developing mechanism wherein the latent charge representing an image selectively attracts small particles of toner which are eventually transferred to a piece of paper and permanently fixed via heat and/or pressure.
These copiers and printers have numerous drawbacks, a few of which are listed below.
1) Black and white laser printers remain
expensive, primarily due to the cost of critical components such as the laser diode, the system optics and associated electronics, and the optical-photoconductor (belt or drum).
2) Color page printers cannot reduce their end user price below $6000.00, in part due to the price of critical components (see 1) above) and in part due to the cost of close tolerance alignment mechanisms to ensure satisfactory production of multiple colors.
3) Laser printers contain a large number of discrete components, each of which can fail, thereby reducing the overall printer reliability.
4) Use of exotic chemicals, both in the manufacture of high technology components for the laser printer and in the working laser printer itself, produces dangerous chemicals which expose workers and end users to health hazards.
5) The user must replace worn out optical-photoconductors, creating a burdensome investment both in time and in money. Additionally, during this replacement process, users must expose themselves to organic polymers having unknown medical effects.
6) Clearly, the size of a laser printer must be greater than the volume of components they contain. Current laser printers, because of the number and bulkiness of their components, cannot be reduced in size to fit comfortably on the desktop, irrespective of the fact that the available room on the desktop is continually shrinking.
7) Most facsimile machines use specially treated paper which most users dislike. Plain paper facsimile machines are significantly more expensive.
Therefore, a need arises for an inexpensive, reliable paper marking device (black and white, or color) having fewer components, requiring no exotic chemicals, and fitting comfortably on a desktop.